Biosensor electrodes prepared by physical vapor deposition

ABSTRACT

A biosensor component is provided that provides enhanced characteristics for use in biosensors, such as blood glucose sensors. The biosensor component comprises a substrate, a conductive layer deposited on the substrate, and a resistive material layer deposited on the conductive layer. The conductive layer includes nickel, chromium, and iron, such that a combined weight percent of the nickel and chromium in the conductive layer is in the range of 25 to less than 95 weight percent, the weight percent of nickel in the conductive layer is at least 8 weight percent, the weight percent of chromium in the conductive layer is at least 10 weight percent, the weight percent of iron in the conductive layer at least 2 weight percent, and such that the conductive layer comprises 0 to 20 weight percent molybdenum.

BACKGROUND Field of the Invention

The present invention is generally related to electrodes, for example,physical vapor deposited components for electrodes such as those foundin biosensors. More particularly, the present invention is related toelectrodes formed with non-noble metal alloys, for example, those foundin biosensor components.

Description of the Related Art

Biosensors for use in analyzing biological samples are becomingincreasingly prevalent. For example, with the rise in cases of diabetesin the world's population, the need for biosensors for measuring bloodglucose has risen dramatically. Such biosensors are generally known asglucometers and operate by having a user place a drop of blood on atest-strip associated with the glucometer. The test-strip is configuredto be reactive to the amount of glucose in the drop of blood, such thatthe glucometer can detect and display a glucose level of the user'sblood.

The test-strips for glucometer-type biosensors are generally formed withtwo or more electrodes (e.g., a working electrode and a counterelectrode) formed on a substrate. In addition, a bio-reactant thatreacts with the biological sample, e.g., an enzyme (e.g., glucoseoxidase, glucose dehydrogenase, or the like), and a mediator (e.g.,ferricyanide, ruthenium complexes, osmium complexes, quinones,phenothiazines, phenoxazines, or the like) will be formed on one or bothelectrodes, e.g., the working electrode. In operation of aglucometer-type biosensor, a drop of blood will be applied to atest-strip. Thereafter, an electrochemical reaction proportional to theamount of glucose in the blood will take place on the working electrode.In more detail, glucose first reacts with the bio-reactant, e.g., enzyme(glucose oxidase, glucose dehyrogenase, or the like) and sometimes anenzyme cofactor (PQQ, FAD, or the like) and is oxidized to gluconicacid. The bio-reactant, e.g., enzyme, cofactor, or enzyme-cofactorcomplex, is temporarily reduced by two electrons transferred fromglucose to the enzyme, cofactor, or enzyme-cofactor complex. Next, thereduced bio-reactant, e.g., enzyme, cofactor, or enzyme-cofactorcomplex, reacts with the mediator, transferring a single electron toeach of two mediator species (molecules or complexes), in the case of amediator that is reduced in a one-electron process. When the mediatorspecies are reduced, the enzyme, cofactor, or enzyme-cofactor complex isthus returned to its original oxidation state. Then, the reducedmediators diffuse to the electrode surface where a pre-determined andsufficiently oxidizing potential is applied to the biosensor so that thereduced mediators are oxidized back to their original oxidation state.The current that is generated by the oxidation of the mediator speciesby the biosensor is measured and related proportionally to the amount ofglucose in the blood.

The quality of the working electrode plays an important role in anaccurate measurement of the glucose level of the blood. Specifically,the reproducibility of the electroactive surface area of the electrode,the lot-to-lot repeatability of the electron transfer kinetics of theelectrode in a particular glucose measurement arrangement, and long termstability of the electrode material while in storage so that theelectrochemical signal that arises from the electrode when the assay isin operation are all factors that lead to improved accuracy of bloodglucose test strips. Particularly, it is important that the electricalsignals resulting from the electro-activity of the electrode isminimized to prevent bias or noise in the measurement and analysis ofbiological samples. Typically, this is accomplished by using electrodematerials that are intrinsically thermodynamically noble, such as gold,palladium, platinum, iridium, and the like. As such, most currentglucometers use electrodes formed from substrates coated with palladium,gold, or other noble metals, generally in the purest form commerciallyfeasible, to function as the working electrode, and for ease ofmanufacturing, often for the counter electrode or a combined counter andreference electrode. Such noble metals are minimally reactive withinterfering substances, and as a result, offer enhanced chemicalresistance for consistent and accurate measurements. However, the costof using such noble metals in electrodes can be prohibitive.

There have been some attempts to use electrodes formed with non-noblemetals, so as to reduce manufacturing costs of biosensors. However, suchnon-noble metal electrodes will generally have an electrochemicalresponse (e.g., dose-responses) that deviates significantly from theelectrochemical response of electrodes formed with noble metals.Non-precious materials typically are not anodically stable enough to beused for electrochemical test strips because of high background currentsgenerated when operating at typical voltages of biosensors. In addition,non-precious materials typically do not have facile heterogeneouselectron transfer with the desired analyte. As such, electrodes formedwith non-noble metals are generally inadequate for use as directreplacements for noble metals in test-strips for many types ofbiosensors. In addition to having a low electrical response, it is alsodesirable for a biosensor electrode to have sufficient electron transferkinetics with the mediator. While some suggested non-noble metals have arelatively low electrochemical response (or reasonable anodicstability), they do not also have acceptable electron transfer kineticswith a mediator.

Accordingly, there is a need for an electrode which can provideconsistent and accurate measurements, while providing a cost effectivealternative to the use of noble metals, for example, in biosensors. Inparticular, there is a need for an electrode formed from a non-noblemetal alloy that can be used in a biosensor component to consistentlyand accurately measure biological samples.

SUMMARY

It has been found that non-precious metals can undergo aging phenomenonwhen exposed to atmospheric conditions resulting in variations in theirperformance for biosensor applications. It has also been found thatelectrodes formed by depositing non-precious metals on a substrate filmto form a conductive layer can be significantly improved by depositing athin layer of resistive material on the conductive layer for biosensorapplications. It has also been found that electrodes formed bydepositing non-precious metals on a substrate film require a sufficientdegree of mechanical robustness to achieve adequate performance forbiosensor applications. Thus, there is a need for an electrode formedfrom a non-noble metal alloy that can be used in a biosensor componentto consistently and accurately measure biological samples, and which hasgood mechanical robustness to allow processing and achieve or maintainelectrical performance.

One or more embodiments of the present disclosure can relate to anelectrode which can comprise a substrate, at least one non-preciousmetal alloy conductive layer deposited on the substrate, and at leastone resistive material layer deposited on the non-precious metal layer.The conductive layer can comprise nickel and chromium wherein thecombined weight percent of the nickel and chromium in the conductivelayer is at least about 50 weight percent, based on the total weight ofthe conductive layer.

In certain embodiments, the conductive layer can comprise nickel andchromium wherein the combined weight percent of the nickel and chromiumin the conductive layer can be at least 60, or at least 70, or at least80, or at least 90, or at least 95 weight percent, based on the totalweight of the conductive layer. In one embodiment, the thickness of theresistive material layer is less than 20 nm. In certain embodiments, theconductive layer can comprise nickel in an amount less than 80 weightpercent and chromium in an amount of greater than 20 weight percent,based on the total weight of the conductive layer. While most of thisdisclosure relates to electrodes used as biosensor components, it iscontemplated that the electrodes can be used in other end-useapplications as well. As a result, any disclosure herein related toelectrodes used in biosensors is intended to incorporate hereinapplicability to all electrodes that this technology could reasonably beapplied to by one of ordinary skill in the art.

In a first aspect, the conductive layer can comprise nickel and chromiumwherein the combined weight percent of the nickel and chromium in theconductive layer can be at least 50, or at least 60, or at least 70, orat least 80, or at least 90, or at least 95 weight percent, based on thetotal weight of the conductive layer equaling 100 weight percent, andthe thickness of the resistive material layer is less than 20 nm.wherein the combined weight percent of the nickel and chromium in theconductive layer is in the range of 90 to 100 weight percent, andwherein the thickness of the resistive layer is in the range from 5 to15 nm.

In embodiments of the first aspect, the resistive material layercomprises amorphous carbon. In certain embodiments, the resistivematerial layer is amorphous carbon deposited by sputtering. In certainembodiments, the resistive material layer is amorphous carbon depositedby sputtering using a solid carbon source.

In embodiments of the first aspect, the resistive material layercomprises amorphous carbon, the weight percent of chromium in theconductive layer is in the range from about 25 to about 95 weightpercent, and the balance of the conductive layer is essentially nickel.

In embodiments of the first aspect, the resistive material layercomprises amorphous carbon, the weight percent of chromium in theconductive layer is in the range from greater than 50 to about 95 weightpercent, and the balance of the conductive layer is essentially nickel.

In embodiments of the first aspect, the resistive material layercomprises amorphous carbon and the resistive material layer has athickness between 5 and 15 nm.

In a second aspect, the conductive layer can comprise nickel andchromium wherein the combined weight percent of the nickel and chromiumin the conductive layer can be at least 50, or at least 60, or at least70, or at least 80, or at least 90, or at least 95 weight percent, basedon the total weight of the conductive layer equaling 100 weight percent,and wherein the conductive layer comprises greater than 20 weightpercent chromium, based on the total weight of the conductive layerequaling 100 weight percent. In embodiments of the second aspect, thesubstrate has a thickness between 25 and 500 μm, the conductive layerhas a thickness between 15 and 200 nm, and the resistive material layerhas a thickness between 5 and 200 nm, or 5 to 100 nm.

In embodiments of the second aspect, the conductive layer can comprisenickel in the range of less than 80 weight percent, or less than 75weight percent, and chromium in the range of greater than 20, or greaterthan 25 weight percent, and wherein the total combined weight percent ofthe nickel and chromium in the conductive layer is in the range of 90 to100, or 95 to 100 weight percent, based on the total weight of theconductive layer equaling 100 weight percent.

In embodiments of the second aspect, the weight percent of chromium inthe conductive layer is in the range from about 25 to about 95 weightpercent, and the balance of the conductive layer is essentially nickel.In other embodiments of the second aspect, the weight percent ofchromium in the conductive layer is in the range from about 30 to about95 weight percent, and the balance of the conductive layer isessentially nickel. In further embodiments of the second aspect, theweight percent of chromium in the conductive layer is in the range fromabout 40 to about 95 weight percent, and the balance of the conductivelayer is essentially nickel. In yet other embodiments of the secondaspect, the weight percent of chromium in the conductive layer is in therange from about 50 to about 95 weight percent, and the balance of theconductive layer is essentially nickel. In another embodiment of thesecond aspect, the weight percent of chromium in the conductive layer isin the range from greater than 50 to about 95 weight percent, and thebalance of the conductive layer is essentially nickel.

In embodiments of the second aspect, the resistive layer is amorphouscarbon. In an embodiment of the second aspect, the resistive layer isamorphous carbon, the weight percent of chromium in the conductive layeris in the range from about 25 to about 95 weight percent, and thebalance of the conductive layer is essentially nickel. In anotherembodiment of the second aspect, the resistive layer is amorphouscarbon, the weight percent of chromium in the conductive layer is in therange from greater than 50 to about 95 weight percent, and the balanceof the conductive layer is essentially nickel. In embodiments of thesecond aspect, the resistive layer is amorphous carbon, and theresistive material layer has a thickness between 5 and 30 nm, or between5 and 20 nm.

In certain embodiments of the present disclosure, the conductive layercan be coated on the substrate, that can be comprised of at least one ofany polymer described in the art and/or described herein including butnot limited to polycarbonate, silicone polymers, acrylics, PET, modifiedPET such as PETG or PCTG, PCT, modified PCT, polyesters comprising TMCDAND CHDM, PCCD, or PEN, by physical vapor deposition.

In certain embodiment of the disclosure, the resistive material layercan comprise a thin film of resistive material deposited on the surfaceof the conductive layer. By the term “resistive material” is meant amaterial that is more electrically resistive than the conductive layer,allows current to flow upon application of a constant potential, and,when formed into a thin film electrode having a conductive layer and aresistive material layer on the conductive layer, increases theelectrode's anodic stability and/or increases electron transferkinetics, as determined by a Type 1 Linear Sweep Voltammetry Test,compared to a similar electrode with just the conductive layer.

In certain embodiments, the resistive material layer can comprise one ormore elements chosen from carbon, silicon, boron, oxygen, andcombinations thereof. In certain embodiments, the resistive materiallayer comprises carbon. In certain embodiments, the resistive materiallayer comprises amorphous carbon. In certain embodiments, the resistivematerial layer is amorphous carbon deposited by sputtering. In certainembodiments, the resistive material layer is amorphous carbon depositedby sputtering using a carbon source. In certain embodiments, theresistive material layer is amorphous carbon deposited by sputteringusing a carbon source in a separate sputtering step than a sputteringstep used to deposit the conductive layer (i.e., there is noco-sputtering of the conductive layer and carbon layer being performed).

In certain embodiments, the resistive layer comprises amorphous carbonthat is composed primarily of sp² hybridized carbon, sp³ hybridizedcarbon, or combinations thereof. In certain embodiments, an amorphouscarbon layer composed primarily of sp² hybridized carbon, sp³ hybridizedcarbon, or combinations thereof can be formed using techniques/processesas suggested by: Onoprienko, A. A., Shaginyan, L. R., Role ofmicrostructure in forming thin carbon film properties. Diamond Relat.Mater. 1994, 3, 1132-1136; Onoprienko, A., In Carbon, The FutureMaterial for Advanced Technology Applications; Messina, G., Santangelo,S., Eds.; Springer Berlin Heidelberg, 2006; or Cho, N. H.; Krishnan, K.M.; Veirs, D. K.; Rubin, M. D.; Hopper, C. B.; Bhushan, B.; Bogy, D. B.Chemical structure and physical properties of diamond-like amorphouscarbon films prepared by magnetron sputtering. J. Mater. Res. 1990, 5,2543-2554.

In certain embodiments of the disclosure, the resistive material layercan have a thickness in the range from 5 to 200 nm, the conductive layercan have a thickness in the range from 15 and 200 nm, and the substratecan have a thickness in the range from 25 and 500 μm. In certainembodiments, the resistive material layer can have a thickness in therange from 5 to less than 20 nm, the conductive layer can have athickness in the range from 15 and 200 nm, and the substrate can have athickness in the range from 25 and 500 μm. In certain embodiments, thebiosensor component can also have visible light transmission of no morethan 20% or no more than 15% or no more than 10% or no more than 5 orfrom 0.01 to 20% or from 0.01 to 15% or from 0.01 10% or from 0.01 to5%, as measured by ASTM D1003.

In certain embodiments of the disclosure, the resistive material layercan have a thickness in the range from 5 to 200 nm, or from 5 to lessthan 20 nm, the conductive layer can have a thickness in the range from15 and 200 nm, and the substrate can have a thickness in the range from25 and 500 μm wherein the biosensor component has a visible lighttransmission of no more than 20%.

In certain embodiments of the disclosure, the resistive material layercan have a thickness in the range from 5 to 200 nm, or from 5 to lessthan 20 nm, the conductive layer can have a thickness in the range from15 and 200 nm, and the substrate can have a thickness in the range from25 and 500 μm wherein the biosensor component has a visible lighttransmission of no more than 15%.

In certain embodiments of the disclosure, the resistive material layercan have a thickness in the range from 5 to 200 nm, or from 5 to lessthan 20 nm, the conductive layer can have a thickness in the range from15 and 200 nm, and the substrate can have a thickness in the range from25 and 500 μm wherein the biosensor component has a visible lighttransmission of no more than 10%.

In certain embodiments of the disclosure, the resistive material layercan have a thickness in the range from 5 to 200 nm, or from 5 to lessthan 20 nm, the conductive layer can have a thickness in the range from15 and 200 nm, and the substrate can have a thickness in the range from25 and 500 μm wherein the biosensor component has a visible lighttransmission of no more than 5%.

In certain embodiments, the resistive material layer has a thickness inthe range from 5 to 100 nm, or 5 to 50 nm, or 5 to 30 nm, or 5 to 25 nm,or 5 to 20 nm, or 5 to less than 20 nm, or 5 to 15 nm. In embodiments,the resistive material layer is amorphous carbon and has a thickness inthe range from 5 to 100 nm, or 5 to 50 nm, or 5 to 30 nm, or 5 to 25 nm,or 5 to 20 nm, or 5 to less than 20 nm, or 5 to 15 nm. In embodiments,the resistive material layer is amorphous carbon and has a thickness inthe range from 5 to 20 nm, or 5 to less than 20 nm, or 5 to 15 nm.

In one aspect, certain embodiments of the present disclosure relate to abiosensor component comprising a substrate, a conductive layer depositedon the substrate, and a resistive material layer deposited on theconductive layer, wherein the resistive material layer can comprisecarbon, the conductive layer can comprise nickel and chromium in acombined weight in the range of 50 to 100 weight percent, chromium in anamount greater than 20 weight percent, nickel in an amount of less than80 weight percent, based on the total weight of the conductive layerequaling 100 weight percent, and the substrate can be comprised of atleast one of any polymer described in the art and/or described hereinincluding but not limited to polycarbonate, silicone polymers, acrylics,PET, modified PET such as PETG or PCTG, PCT, PCTA, polyesters comprisingTMCD AND CHDM, PCCD, or PEN, by any means known in the art, includingbut not limited to, physical vapor deposition. The resistive layer canhave a thickness in the range of 5 to 100 nm, or 5 to less than 20 nm,the conductive layer can have a thickness of between 15 and 200 nm, andthe substrate can have a thickness of between 25 and 500 μm, such thatthe biosensor component has a visible light transmission of no more than20% or no more than 15% or no more than 10% or no more than 5%.

In one aspect, certain embodiments of the present disclosure relate to abiosensor component comprising a substrate, a conductive layer depositedon the substrate, and a resistive material layer deposited on theconductive layer, wherein the resistive material layer can comprisecarbon, the conductive layer can comprise nickel and chromium in acombined weight in the range of at least 50, or at least 60, or at least70, or at least 80, or at least 90, or at least 95 weight percent, basedon the total weight of the conductive layer equaling 100 weight percent,and the thickness of the resistive material layer is less than 20 nm,and the substrate can be comprised of at least one of any polymerdescribed in the art and/or described herein including but not limitedto polycarbonate, silicone polymers, acrylics, PET, modified PET such asPETG or PCTG, PCT, PCTA, polyesters comprising TMCD AND CHDM, PCCD, orPEN, by any means known in the art, including but not limited to,physical vapor deposition. The resistive layer can have a thickness inthe range of 5 to less than 20 nm, or 5 to 15 nm, the conductive layercan have a thickness of between 15 and 200 nm, and the substrate canhave a thickness of between 25 and 500 μm, such that the biosensorcomponent has a visible light transmission of no more than 20% or nomore than 15% or no more than 10% or no more than 5%.

One or more embodiments of the present disclosure can related to anelectrode for a biosensor, with the electrode comprising a substrate, aconductive layer deposited on the substrate, and a resistive materiallayer deposited on the conductive layer. In certain embodiments, theconductive layer can comprise nickel and chromium, and the conductivelayer can have an oxidation wave voltage for Fe(II)[CN]₆ mediator(identified below as E_(peak,anodic)) of less than 450, or less than400, or less than 375, or less than 350, or less than 325, or less than300, or less than 275 millivolts (mV), as determined in a Type 1 LinearSweep Voltammetry Test (as discussed in the Examples section).

The substrate can be comprised of any polymer composition known in theart including but not limited to at least one polymer selected from thegroups consisting of: nylon, polyesters, copolyesters, polyethylene,polypropylene, polyamides; polystyrene, polystyrene copolymers, styreneacrylonitrile copolymers, acrylonitrile butadiene styrene copolymers,poly(methylmethacrylate), acrylic copolymers, poly(ether-imides);polyphenylene oxides or poly(phenylene oxide)/polystyrene blends,polystyrene resins; polyphenylene sulfides; polyphenylenesulfide/sulfones; poly(ester-carbonates); polycarbonates; polysulfones;polysulfone ethers; and poly(ether-ketones); or mixtures of any of theother foregoing polymers.

In one embodiment, the substrate can be comprised of at least onepolyester comprising residues of at least one glycol selected from thegroup consisting of ethylene glycol, 1,4-cyclohexanedimethanol, and2,2,4,4-tetramethyl-1,3-cyclobutanediol.

In one embodiment, the substrate can be comprised of at least onepolyester comprising residues of terephthalic acid and/or dimethylterephthalate and residues of at least one glycol selected from thegroup consisting of ethylene glycol, 1,4-cyclohexanedimethanol, and2,2,4,4-tetramethyl-1,3-cyclobutanediol.

In one embodiment, the substrate can be comprised of at least onepolyester comprising an acid component which comprises residues ofterephthalic acid and isophthalic acid and/or esters thereof such asdimethyl terephthalate, and at glycol component comprising residues ofat least one glycol selected from the group consisting of ethyleneglycol residues, 1,4-cyclohexanedimethanol residues, and2,2,4,4-tetramethyl-1,3-cyclobutanediol.

In one embodiment, the substrate can be comprised of at least onepolyester comprising terephthalic acid residues, or an ester thereof, ormixtures thereof, and 1, 4-cyclohexanedimethanol residues.

In one embodiment, the substrate can be comprised of at least onepolyester made from terephthalic acid residues, or an ester thereof, ormixtures thereof, and 1,4-cyclohexanedimethanol residues and/or2,2,4,4-tetramethyl-1, 3-cyclobutanediol residues.

In one embodiment, the substrate can be comprised of at least onepolyester made from terephthalic acid residues, or an ester thereof, ormixtures thereof, 2,2,4,4-tetramethyl-1, 3-cyclobutanediol residues, and1,4-cyclohexanedimethanol residues.

In one embodiment, the substrate can be comprised of at least onepolyester made from terephthalic acid residues, or an ester thereof, ormixtures thereof, 2,2,4,4-tetramethyl-1,3-cyclobutanediol residues, andethylene glycol residues.

In one embodiment, the substrate can be comprised of at least onepolyester comprising terephthalic acid residues, or an ester thereof, ormixtures thereof, ethylene glycol residues, and 1,4-cyclohexanedimethanol residues.

Conductive layers in the present disclosure can be constructed of asingle layer comprising any of the alloy compositions disclosed in thisapplication. In certain embodiments, the alloy composition contains analloy which can be a solid solution of the elements (a single phase), amixture of metallic phases (two or more solutions) or an intermetalliccompound with no distinct boundary between the phases.

One or more embodiments of the present disclosure concern a method forforming an electrode for a biosensor. The method comprises (a) providinga substrate; (b) providing a conductive layer target; (c) physical vapordepositing at least a portion of said substrate with material from saidconductive layer target to thereby form a conductive layer on saidsubstrate having a conductive layer surface facing opposite thesubstrate; (d) providing a target that when used as the source materialfor physical vapor deposition, produces a resistive material hereafterreferred to as “resistive material target”; and (e) physical vapordepositing at least a portion of said conductive layer with materialfrom said resistive material target to thereby form a resistive materiallayer on said conductive layer surface. The conductive material cancomprise nickel and chromium wherein the combined weight percent of thenickel and chromium in the conductive layer can be at least 50, or atleast 60, or at least 70, or at least 80, or at least 90, or at least 95weight percent. In certain embodiments, the resistive material layer cancomprise amorphous carbon and have a thickness in the range from 5 to100 nm, or 5 to 50 nm, or 5 to 25 nm, or 5 to less than 20 nm. In oneembodiment, the resistive material layer can comprise amorphous carbonand have a thickness in the range from 5 to less than 20 nm. In oneembodiment, the conductive material can comprise nickel and chromium,wherein the chromium in present in an amount of greater than 20 weightpercent, or at least 25 weight percent, and the resistive material layercan comprise amorphous carbon and have a thickness in the range from 5to 100 nm. Additionally, the combined conductive layer and resistivematerial layer can have a sheet resistance of less than 2000 ohms persquare.

One or more embodiments of the present disclosure concern a method forforming an electrode for a biosensor. The combined conductive layer andresistive material layer can have a sheet resistance, as measured byASTM F1711-96, of no more than 5000, 2000, 100, 80, 60, 50, 40, 20, 10,or 5 ohms per square. In some embodiments, the layers can have a sheetresistance of between 1 to 5000 ohms per square, 1 to 4000 ohms persquare, 1 to 3000 ohms per square, 1 to 2000 ohms per square, 1 to 1000ohms per square, 1 to 500 ohms per square, 5 to 100 ohms per square, 5to 20 ohms per square, 5 to 15 ohms per square, 5 to 10 ohms per square,10 to 80 ohms per square, 20 to 60 ohms per square, or 40 to 50 ohms persquare, as measured by ASTM F1711-96. The layers can have a sheetresistance of less than 2000 ohms per square.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the present disclosure are described herein withreference to the following figures, wherein:

FIG. 1 is a sectional schematic illustration of a thin-film electrodebiosensor component of embodiments of the present disclosure;

FIG. 2 is a schematic illustration of a test-strip biosensor componentof embodiments of the present disclosure;

FIG. 3 is a graph depicting a linear sweep voltammogram plot of athin-film electrode in a mediator-containing solution;

FIG. 4 is a graph depicting a linear sweep voltammogram plot ofthin-film electrodes comparing various NiCr metal alloy conductivelayers capped by carbon in Fe(II)[CN]₆ mediator-containing buffersolutions;

FIG. 5 is a graph depicting the average E_(peak,anodic) value forvarious NiCr metal alloy conductive layers capped by carbon inFe(II)[CN]₆ mediator-containing buffer solutions;

FIG. 6 is a graph depicting a linear sweep voltammogram plot ofthin-film electrodes comparing NiCr metal alloy conductive layerscontaining 40 and 80 weight % Ni, respectively, each capped by carbon inFe(II)[CN]₆ mediator-containing buffer solutions;

FIG. 7 is a graph depicting the effect of bending thin-film electrodeover various diameter mandrels (coated side touching) on sheetresistance for various NiCr conductive layer alloys capped with carbon.

DETAILED DESCRIPTION

The present invention is generally directed to a component for anelectrode such as those used in a biosensor. As used herein, the term“biosensor” shall denote a device for analyzing biological samples. Insome embodiments, as illustrated in FIG. 1, the biosensor component maybe a layered thin-film electrode 100 and may broadly comprise asubstrate 102, a conductive layer 104 deposited on at least a portion ofthe substrate 102, and a resistive material layer 106 deposited on atleast a portion of the conductive layer 104. In some embodiments, thebiosensor may be a medical sensor, such as a glucose measuring system,and the biosensor component may be a test-strip for use with thebiosensor. As used herein, the term “medical sensor” shall denote abiosensor used for medical monitoring and/or diagnosis. For instance, asillustrated in FIG. 2, some embodiments contemplate that the biosensorcomponent will comprise a test-strip 110 that includes a first electrode100 separated from a second electrode 100 a by a reaction space 112. Thefirst electrode 100 may comprise a working electrode and the secondelectrode 100 a may comprise a reference electrode or a counterelectrode or a combined reference and counter electrode. As such, abiological sample, such as a drop of blood, can be placed within thereaction space 112 and in electrical contact with the first and secondelectrodes 100 and 100 a for analysis. It should be understood that FIG.2 is not intended to be limiting and shows one possible embodiment for atest strip. Other embodiments for test strips can include differentconfigurations for the electrode(s), such as, for example, a co-planarelectrode configuration. As used herein, the term “blood glucose sensor”shall denote a medical sensor used to determine a concentration ofglucose in blood. In addition, a bio-reactant that reacts with thebiological sample, e.g., a protein, an enzyme (e.g., glucose oxidase,glucose dehydrogenase, or the like), and a mediator (e.g., ferricyanide,ruthenium complexes, osmium complexes, quinones, phenothiazines,phenoxazines, or the like) can be formed on one or both electrodes,e.g., the working electrode.

Unlike conventional physical vapor deposited biosensor components, whichnormally include and/or use noble metals such as palladium and/or gold,the biosensor components described herein can be formed from non-noblemetals alloys, such as those including nickel and chromium.Nevertheless, biosensor components, such as thin-film electrodes, formedfrom the non-noble metals alloys having a resistive material layerdeposited thereon, as described herein, can exhibit superior consistencyand accuracy when measuring biological samples. Thus, by using biosensorcomponents comprised of the non-noble metal alloys and a resistivematerial layer, as described herein, the material and manufacturingcosts typically associated with the fabrication and use of biosensorcomponents can be significantly reduced.

Embodiments of the present disclosure provide for the substrate 102 tobe formed from any type of material, either flexible or rigid, which isgenerally non-conductive and chemically inert to the contemplatedchemical reactions described herein. In certain embodiments, thesubstrate 102 of the biosensor component may comprise a flexible,non-conductive film, including polymers, such as a polymeric film, apolyester film, a polycarbonate film, or the like. In certain specificembodiments, the substrate 102 may comprise a polyethylene terephthalate(PET) film. Embodiments of the present disclosure contemplate that thesubstrate 102 may have a thickness of at least 25 μm, 125 μm, or 250 μm,and/or not more than 800 μm, 500 μm, or 400 μm. In certain embodiments,the substrate 102 may have a thickness of between 25 to 800 μm, 25 to500 μm, or 25 to 400 μm, between 125 to 800 μm, 125 to 500 μm, or 125 to400 μm, or between 250 to 800 μm, 250 to 500 μm, or 250 to 400 μm.

The conductive layer 104 coated on the substrate 102 may comprise one ormore non-noble metals. Such conductive layer 104 may be coated on thesubstrate 102 via one or more physical vapor deposition techniques, suchas sputter coating (e.g., magnetron sputtering, unbalanced magnetronsputtering, facing targets sputtering, or the like), thermalevaporation, electron beam evaporation, laser ablation, arcvaporization, co-evaporation, ion plating, or the like. The conductivelayer 104 may be coated on the substrate 102 to a thickness of at least1, 10, 15, or 30 nm, and/or not more than 1000, 200, 100, or 50, nm. Incertain embodiments, the conductive layer 104 may have a thickness ofbetween 1 to 1000 nm, 1 to 200 nm, 1 to 100 nm, or 1 to 50 nm, between10 to 1000 nm, 10 to 200 nm, 10 to 100 nm, or 10 to 50 nm, between 15 to1000 nm, 15 to 200 nm, 15 to 100 nm, or 15 to 50 nm, or between 30 to1000 nm, 30 to 200 nm, 30 to 100 nm, or 30 to 50 nm.

The resistive material layer 106 may be deposited on the conductivelayer 104 via one or more physical vapor deposition techniques, such assputter coating (e.g., magnetron sputtering, unbalanced magnetronsputtering, facing targets sputtering, or the like), thermalevaporation, electron beam evaporation, arc vaporization,co-evaporation, ion plating, plasma enhanced vapor deposition, atomiclayer deposition, or the like. In certain embodiments, the resistivematerial layer 106 may be coated on the substrate 104 to a thickness ofat least 1, 5, 10, or 15 nm, and/or not more than 200, 100, 50, 25, 20,an amount less than 20, or 15 nm. In certain embodiments, the resistivelayer 106 may have a thickness of from 1 to 200 nm, 1 to 100 nm, 1 to 50nm, 1 to 20 nm, 1 to less than 20 nm, or 1 to 15 nm; or from 5 to 200nm, 5 to 100 nm, 5 to 50 nm, 5 to 25 nm, 5 to 20 nm, 5 to less than 20nm, or 5 to 15 nm; or from 10 to 200 nm, 10 to 100 nm, 10 to 50 nm, or10 to 25 nm, 10 to 20 nm, 10 to less than 20 nm, or 10 to 15 nm. Inembodiments, resistive layer 106 may have a thickness of from 1 to lessthan 20 nm, or 1 to 19 nm, or 1 to 18 nm, or 1 to 17 nm, or 1 to 16 nm,or 5 to 19 nm, or 5 to 18 nm, or 5 to 17 nm, or 5 to 16 nm, or 7 to 19nm, or 7 to 18 nm, or 7 to 17 nm, or 7 to 16 nm, or 10 to 19 nm, or 10to 18 nm, or 10 to 17 nm, or 10 to 16 nm.

The conductive layer 104 and resistive material layer 106 may bedeposited on the substrate 102, such that the resulting thin-filmelectrode 100 will generally be opaque to visible light. For example,the resulting thin-film electrode 100 may have a visible lighttransmission, as measured by ASTM D1003, of no more than 50%, no morethan 40%, no more than 30%, or no more than 20%. In certain embodiments,the resulting thin-film electrode 100 may have a visible lighttransmission of between 1 to 50%, between 10 to 40%, between 15 to 30%,or about 20%. Additionally, the resulting thin-film electrode 100 mayhave a sheet resistance, as measured by ASTM F1711-96, of no more than5000, 2000, 100, 80, 60, 50, 40, 20, 10, or 5 ohms per square. In someembodiments, the resulting thin-film electrode 100 may have a sheetresistance of between 1 to 5000 ohms per square, 2 to 2000 ohms persquare, 5 to 100 ohms per square, 10 to 80 ohms per square, 20 to 60ohms per square, or 40 to 50 ohms per square.

Non-noble metals described herein, which form a conductive layer 104,may be comprised of alloys of nickel and chromium. For example,non-noble metal alloys comprised of at least 5 weight percent nickel andat least 5 weight percent Cr were used to prepare conductive layers 104of a biosensor component, wherein the conductive layers were furthercoated by depositing an amorphous carbon resistive material layer 106 onthe conductive layer 104. Various alloys containing nickel and chromiumranging from Ni:Cr (weight) ratio of 100:0 to 0:100 were used to prepareelectrodes comprising both a conductive layer and an amorphous carbonresistive material layer.

In certain embodiments, the amount of nickel and chromium included inthe non-noble metal alloys that comprise the conductive layer of theelectrode (for example, conductive layer 104 of the biosensor component)can vary depending on the specific requirements of the electrode, forexample, the biosensor component. In various embodiments, the non-noblemetal alloys can comprise at least about 5 to about 95 weight percent ofnickel. Additionally, in various embodiments, the non-noble metal alloyscan comprise at least about 5, 10, 20, greater than 20, 25, 30, 40, 50,or greater than 50, 60 and/or up to about 95, 90, 80, 70, 60, greaterthan 50, 50, or 40 weight percent of chromium. More particularly, inembodiments, the non-noble metal alloys can comprise in the range ofabout 5 to 95, 10 to 90, 10 to 80, 10 to 70, 10 to 60, 10 to 50, 10 to40, 20 to 90, 20 to 80, 20 to 70, 20 to 60, 20 to 50, 20 to 40, greaterthan 20 to 90, greater than 20 to 80, greater than 20 to 70, greaterthan 20 to 60, greater than 20 to 50, greater than 20 to 40, 25 to 90,25 to 80, 25 to 70, 25 to 60, 25 to 50, 25 to 40, 30 to 90, 30 to 80, 30to 70, 30 to 60, 30 to 50, 30 to 40, 40 to 90, 40 to 80, 40 to 70, 40 to60, 40 to 50, 50 to 90, 50 to 80, 50 to 70, 50 to 60, greater than 50 to95, greater than 50 to 90, greater than 50 to 80, greater than 50 to 70,greater than 50 to 60, 60 to 95, 60 to 90, 60 to 80, 60 to 70, 70 to 95,70 to 90, 70 to 80, 80 to 95, or 80 to 90 weight percent of chromium. Inone embodiment, in addition to the amount of chromium as specifiedabove, the balance of the alloy is nickel. It should be understood thatalloys containing nickel and chromium in a combined amount of 100 weightpercent of the alloy, the alloy can still contain a small amount ofother elements as impurities.

In certain embodiments, the amount of nickel and chromium included inthe non-noble metal alloys that comprise the conductive layer ofelectrode, for example, the biosensor component, can vary depending onthe specific requirements of the biosensor component as follows: 10 to95 weight % chromium and 5 to 90 weight % nickel; 10 to 90 weight %chromium and 10 to 90 weight % nickel; or 10 to 80 weight % chromium and20 to 90 weight % nickel; or 10 to 70 weight % chromium and 30 to 90weight % nickel; or 10 to 60 weight % chromium and 40 to 90 weight %nickel; or 10 to 50 weight % chromium and 50 to 90 weight % nickel, or10 to 40 weight % chromium and 60 to 90 weight % nickel; or 20 to 90weight % chromium and 10 to 80 weight % nickel; or 20 to 80 weight %chromium and 20 to 80 weight % nickel; or 20 to 70 weight % chromium and30 to 80 weight % nickel; or 20 to 60 weight % chromium and 40 to 80weight % nickel; or 20 to 50 weight % chromium and 50 to 80 weight %nickel; or 20 to 40 weight % chromium and 60 to 80 weight nickel; orgreater than 20 to 90 weight % chromium and 10 to less than 80 weight %nickel; or greater than 20 to 80 weight % chromium and 20 to less than80 weight % nickel; or greater than 20 to 70 weight % chromium and 30 toless than 80 weight % nickel; or greater than 20 to 60 weight % chromiumand 40 to less than 80 weight % nickel; or greater than 20 to 50 weight% chromium and 50 to less than 80 weight % nickel; or greater than 20 to40 weight % chromium and 60 to less than 80 weight % nickel; or 25 to 90weight % chromium and 10 to 75 weight % nickel; or 25 to 80 weight %chromium and 20 to 75 weight % nickel; or 25 to 70 weight % chromium and30 to 75 weight % nickel; or 25 to 60 weight % chromium and 40 to 75weight % nickel; or 25 to 50 weight % chromium and 50 to 75 weight %nickel; or 25 to 40 weight % chromium and 60 to 75 weight % nickel; or30 to 90 weight % chromium and 10 to 70 weight % nickel; or 30 to 80weight % chromium and 20 to 70 weight % nickel; or 30 to 70 weight %chromium and 30 to 70 weight % nickel; or 30 to 60 weight % chromium and40 to 70 weight % nickel; or 30 to 50 weight % chromium and 50 to 70weight % nickel; or 30 to 40 weight % chromium and 60 to 70 weight %nickel; or 40 to 90 weight % chromium and 10 to 60 weight % nickel; or40 to 80 weight % chromium and 20 to 60 weight % nickel; or 40 to 70weight % chromium and 30 to 60 weight % nickel; or 40 to 60 weight %chromium and 40 to 60 weight % nickel; or 40 to 50 weight % chromium and50 to 60 weight % nickel; or 50 to 95 weight % chromium and 5 to 50weight % nickel; 50 to 90 weight % chromium and 10 to 50 weight %nickel; or 50 to 80 weight % chromium and 20 to 50 weight % nickel; or50 to 70 weight % chromium and 30 to 50 weight % nickel; or 50 to 60weight % chromium and 40 to 50 weight % nickel; or greater than 50 to 95weight % chromium and 5 to less than 50 weight % nickel; or greater than50 to 90 weight % chromium and 10 to less than 50 weight % nickel; orgreater than 50 to 80 weight % chromium and 20 to less than 50 weight %nickel; or greater than 50 to 70 weight % chromium and 30 to less than50 weight % nickel; or greater than 50 to 60 weight % chromium and 40 toless than 50 weight % nickel; or 60 to 95 weight % chromium and 5 to 40weight % nickel; or 60 to 90 weight % chromium and 10 to 40 weight %nickel; or 60 to 80 weight % chromium and 20 to 40 weight % nickel; or60 to 70 weight % chromium and 30 to 40 weight % nickel; or 70 to 95weight % chromium and 5 to 30 weight % nickel; or 70 to 90 weight %chromium and 10 to 30 weight % nickel; or 70 to 80 weight % chromium and20 to 30 weight % nickel; or 80 to 95 weight % chromium and 5 to 20weight % nickel; or 80 to 90 weight % chromium and 10 to 20 weight %nickel; all of these weight percentages being based on the total weightpercentages of the conductive layer equaling 100 weight percent.

In certain embodiments, the conductive layer contains molybdenum, ifpresent, in an amount of 0 to 2, or 0 to 1 weight percent, based on thetotal weight of the conductive layer. In certain embodiments, theconductive layer contains molybdenum, if present, in an amount less than1, or less than 0.8, or less than 0.6, or less than 0.4, or less than0.2, or less than 0.1 weight percent, based on the total weight of theconductive layer. In embodiments, the conductive layer is substantiallyfree of molybdenum. In embodiments, the conductive layer contains nomolybdenum.

In certain embodiments, the conductive layer contains less than 1.0, orless than 0.5, or less than 0.2 weight percent of each of the followingelement species: iron, carbon, sulfur, phosphorous, molybdenum, niobium,cobalt, aluminum, titanium, or boron. In an embodiment, the conductivelayer contains none, or is substantially free, of the following elementspecies: carbon, sulfur, phosphorous, molybdenum, niobium, cobalt,aluminum, titanium, or boron. In certain embodiments, the conductivelayer comprises nickel and chromium and contains less than 1.0, or lessthan 0.5, or less than 0.2, or less than 0.1, or less than 0.05 weightpercent of any other element species. In certain embodiments, theconductive layer comprises nickel and chromium and contains less than2.0, or less than 1.0, or less than 0.5, or less than 0.2, or less than0.1, or less than 0.05 weight percent of a total of all other elementspecies.

In certain embodiments, the amount of nickel and chromium included inthe non-noble metal alloys that comprise the conductive layer of theelectrode, for example, the biosensor component, can vary depending onthe specific requirements of the biosensor component as follows: 10 to95 weight % chromium and 5 to 90 weight % nickel; 10 to 90 weight %chromium and 10 to 90 weight % nickel; or 10 to 80 weight % chromium and20 to 90 weight % nickel; or 10 to 70 weight % chromium and 30 to 90weight % nickel; or 10 to 60 weight % chromium and 40 to 90 weight %nickel; or 10 to 50 weight % chromium and 50 to 90 weight % nickel, or10 to 40 weight % chromium and 60 to 90 weight % nickel; or 20 to 90weight % chromium and 10 to 80 weight % nickel; or 20 to 80 weight %chromium and 20 to 80 weight % nickel; or 20 to 70 weight % chromium and30 to 80 weight % nickel; or 20 to 60 weight % chromium and 40 to 80weight % nickel; or 20 to 50 weight % chromium and 50 to 80 weight %nickel; or 20 to 40 weight % chromium and 60 to 80 weight % nickel; orgreater than 20 to 90 weight % chromium and 10 to less than 80 weight %nickel; or greater than 20 to 80 weight % chromium and 20 to less than80 weight % nickel; or greater than 20 to 70 weight % chromium and 30 toless than 80 weight % nickel; or greater than 20 to 60 weight % chromiumand 40 to less than 80 weight % nickel; or greater than 20 to 50 weight% chromium and 50 to less than 80 weight % nickel; or greater than 20 to40 weight % chromium and 60 to less than 80 weight % nickel; or 25 to 90weight % chromium and 10 to 75 weight % nickel; or 25 to 80 weight %chromium and 20 to 75 weight % nickel; or 25 to 70 weight % chromium and30 to 75 weight % nickel; or 25 to 60 weight % chromium and 40 to 75weight % nickel; or 25 to 50 weight % chromium and 50 to 75 weight %nickel; or 25 to 40 weight % chromium and 60 to 75 weight % nickel; or30 to 90 weight % chromium and 10 to 70 weight % nickel; or 30 to 80weight % chromium and 20 to 70 weight % nickel; or 30 to 70 weight %chromium and 30 to 70 weight % nickel; or 30 to 60 weight % chromium and40 to 70 weight % nickel; or 30 to 50 weight % chromium and 50 to 70weight % nickel; or 30 to 40 weight % chromium and 60 to 70 weight %nickel; or 40 to 90 weight % chromium and 10 to 60 weight % nickel; or40 to 80 weight % chromium and 20 to 60 weight % nickel; or 40 to 70weight % chromium and 30 to 60 weight % nickel; or 40 to 60 weight %chromium and 40 to 60 weight % nickel; or 40 to 50 weight % chromium and50 to 60 weight % nickel; or 50 to 95 weight % chromium and 5 to 50weight % nickel; 50 to 90 weight % chromium and 10 to 50 weight %nickel; or 50 to 80 weight % chromium and 20 to 50 weight % nickel; or50 to 70 weight % chromium and 30 to 50 weight % nickel; or 50 to 60weight % chromium and 40 to 50 weight % nickel; or greater than 50 to 95weight % chromium and 5 to less than 50 weight % nickel; or greater than50 to 90 weight % chromium and 10 to less than 50 weight % nickel; orgreater than 50 to 80 weight % chromium and 20 to less than 50 weight %nickel; or greater than 50 to 70 weight % chromium and 30 to less than50 weight % nickel; or greater than 50 to 60 weight % chromium and 40 toless than 50 weight % nickel; or 60 to 95 weight % chromium and 5 to 40weight % nickel; or 60 to 90 weight % chromium and 10 to 40 weight %nickel; or 60 to 80 weight % chromium and 20 to 40 weight % nickel; or60 to 70 weight % chromium and 30 to 40 weight % nickel; or 70 to 95weight % chromium and 5 to 30 weight % nickel; or 70 to 90 weight %chromium and 10 to 30 weight % nickel; or 70 to 80 weight % chromium and20 to 30 weight % nickel; or 80 to 95 weight % chromium and 5 to 20weight % nickel; or 80 to 90 weight % chromium and 10 to 20 weight %nickel; all of these weight percentages being based on the total weightpercentages of the conductive layer equaling 100 weight percent; andwherein the conductive layer comprises nickel and chromium and containsless than 1.0, or less than 0.5, or less than 0.2 weight percent of anyother element species, or is substantially free of any other elementspecies, or contains no other element species.

Conductive layers in the present disclosure can be constructed of asingle layer comprising any of the alloy compositions disclosed in thisapplication. In certain embodiments, the alloy composition contains analloy which can be a solid solution of the elements (a single phase), amixture of metallic phases (two or more solutions) or an intermetalliccompound with no distinct boundary between the phases.

As one skilled in the art would readily appreciate, the elements of thenon-noble metal alloys may comprise incidental impurities. As usedherein, “incidental impurities” refer to any impurities that naturallyoccur in the ore used to the produce the non-noble metal alloys or thatare inadvertently added during the production process. The non-noblemetal alloys can comprise less than about 0.1, 0.05, or 0.001 weightpercent of the incidental impurities.

The non-noble metal alloys described herein may also contain one or moreadditional alloying elements, which are in addition to the elementsdescribed above. However, in various embodiments, the non-noble metalalloys can be substantially free from such additional alloying elements.As used herein, the terms “practically free” and “substantially free”mean that the non-noble metal alloy comprises less than 0.001 weightpercent of such additional alloying components. Furthermore, the terms“practically free” and “substantially free” may be used interchangeably.

In certain embodiments of the present disclosure, the biosensorcomponents described herein can be prepared by performing the followingsteps:

(a) providing a substrate;

(b) providing a conductive layer target;

(c) physical vapor depositing at least a portion of the substrate withmaterial from the target to thereby form a conductive layer on thesubstrate;

(d) providing a resistive material target;

(e) physical vapor depositing at least a portion of the conductive layerwith material from the resistive material target to thereby form aresistive material layer on the substrate.

The providing a substrate of step (a) may include the provision of anytype of substrate material, such as PET, as was previously described. Incertain embodiments, the substrate will comprise a sheet of substratematerial that can be actuated within a high vacuum chamber. The sheet ofsubstrate material may comprise a single section of material, such as asquare sheet. In some other embodiments, sheet of substrate material maycomprise a roll of material that is passed, via a roll-to-rollmechanism, through the high vacuum chamber, as will be described in moredetail below. In other embodiments, the substrate may be held stationaryor may be rotated during deposition, as will be also described below.

The providing a target of step (b) may include the provision of aphysical vapor deposition target comprised of any of the non-noble metalalloys previously described. For example, in some embodiments, thephysical vapor deposition targets comprising the alloys of nickel andchromium, as discussed herein, were used to make thin film conductivelayers. Such alloy targets may comprise less than about 0.1, 0.05, or0.001 weight percent of incidental impurities. In some embodiments, thephysical vapor deposition target will be housed within and/or willcomprise an electrode, such as a sputter cathode, during the physicalvapor deposition process. In certain embodiments, the physical vapordeposition target may be a circular, having a diameter of at least 2, 4,8, 12, 16, or 20 cm. In other embodiments, the physical vapor depositiontarget may be a tubular target having an inner diameter of at least 2,4, 8, or 16 cm and an outer diameter of 20, 24, 28 or 32 cm. In stillother embodiments, the physical vapor deposition target may berectangular with dimensions of: a width of between 5 to 25 cm, a lengthof between 25 to 75 cm, and a thickness of between 0.3 to 5 cm. Itshould be understood, however, that embodiments of the presentdisclosure contemplate the use of other-shaped and sized targets.

The physical vapor depositing of step (c) generally includes the coatingof the substrate with the material from the non-noble metal alloy targetto form the conductive layer. As used herein, the term “physical vapordeposition” shall denote depositing thin-films by providing for thecondensation of vaporized material onto a substrate. The physical vapordeposited coating may be performed with any type of physical vapordeposition process previously described, i.e., sputter coating, thermalevaporation, electron beam evaporation, laser ablation, arcvaporization, co-evaporation, ion plating, or the like. For example, insome embodiments, the physical vapor depositing step will be performedvia a sputtering process, in which the substrate is coated with theconductive layer by sputtering the non-noble metal alloy target via thesputtering device. Specific examples of such a sputtering-type physicalvapor depositing will be described in more detail below. The resultingsubstrate with the conductive layer coated thereon may be used as abiosensor component, such as an electrode. Such electrodes may include aworking electrode, a reference electrode, and/or a counter electrode. Incertain embodiments, such as when a roll of substrate material is vacuumcoated with a conductive layer, via a roll-to-roll physical vapordeposition process, the resulting thin-film sheet may be cut apart toappropriate size to form a thin-film electrode specifically sized forthe biosensor component. In other embodiments, the biosensor componentscan be formed from the thin-film sheet by etching, such as chemical orlaser etching. In still other embodiments, the biosensor components canbe formed using a patterned mask, which is laid on the substrate, andthe conductive layer is physical vapor deposited thereover to form theconductive layer of a biosensor component.

The providing a target of step (d) may include the provision of aphysical vapor deposition target comprised of any of the resistivematerials previously described. For example, in some embodiments, thephysical vapor deposition targets comprising carbon were used to makethin film amorphous carbon layers. Such resistive material targets maycomprise less than about 0.1, 0.05, or 0.001 weight percent ofincidental impurities. In embodiments, a target can include materialsthat can differ from the deposited resistive layer but, when used as thesource material for physical vapor deposition, produce the resistivematerial. It should be understood that the resistive material target canhave a different composition and/or structure than the depositedresistive material. In some embodiments, the physical vapor depositiontarget will be housed within and/or will comprise an electrode, such asa sputter cathode, during the physical vapor deposition process. Incertain embodiments, the physical vapor deposition target may be acircular, having a diameter of at least 2, 4, 8, 12, 16, or 20 cm. Inother embodiments, the physical vapor deposition target may be a tubulartarget having an inner diameter of at least 2, 4, 8, or 16 cm and anouter diameter of 20, 24, 28 or 32 cm. In still other embodiments, thephysical vapor deposition target may be rectangular with dimensions of:a width of from 5 to 25 cm, a length of between 25 to 75 cm, and athickness of from 0.3 to 5 cm. It should be understood, however, thatembodiments of the present disclosure contemplate the use ofother-shaped and sized targets.

The physical vapor depositing of step (e) generally includes the coatingof the substrate with the material from the resistive material target toform the resistive material layer. As used herein, the term “physicalvapor deposition” shall denote depositing thin-films by providing forthe condensation of vaporized material onto a substrate. The physicalvapor deposited coating may be performed with any type of physical vapordeposition process previously described, e.g., sputter coating, thermalevaporation, electron beam evaporation, arc vaporization,co-evaporation, ion plating, or the like. For example, in someembodiments, the physical vapor depositing step will be performed via asputtering process, in which the conductive layer (previously depositedon the substrate) is coated with the resistive material layer bysputtering the resistive material target via the sputtering device.Specific examples of such a sputtering-type physical vapor depositingwill be described in more detail below. The resulting substrate with theconductive layer and resistive material layer coated thereon may be usedas a biosensor component, such as an electrode. In embodiments, the“resistive material” layer is a generally distinct layer from theconductive layer, forming a laminar structure, where there is a distinctinterface between the layers so that each of the resistive materiallayer and conductive layer are separate and distinct layers, havingdifferent compositions.

In certain embodiments, such as when a roll of substrate material isvacuum coated with a conductive layer, via a roll-to-roll physical vapordeposition process, the resulting thin-film sheet may be cut apart toappropriate size to form a thin-film electrode specifically sized forthe biosensor component. Such electrodes may include a workingelectrode, a reference electrode, and/or a counter electrode. Electrodesmay also include those for the detection of conductivity of a sample,whether or not a sample has been applied to the biosensor component, orother electrical characteristics of the sample or sample environmentthat is useful for a biosensor. In other embodiments, the biosensorcomponents can be formed from the thin-film sheet by etching, such aschemical or laser etching. In still other embodiments, the biosensorcomponents can be formed using a patterned mask, which is laid on thesubstrate and conductive layer, and the resistive material layer isphysical vapor deposited thereover to form the biosensor component.

In certain specific embodiments, the biosensor components may be createdvia a roll-to-roll physical vapor deposition process that includesroll-to-roll magnetron sputtering. For instance, a substrate sheetcomprising a polymer film made of PET (polyethylene terepthalate) with athickness ranging from 25 μm to 250 μm and width of 33.02 cm may besputtered using a 77.50 cm wide web roll-to-roll magnetron sputtercoater, such as a the Smartweb coater offered by Applied Materials, Inc.or the Mark 80 offered by CHA Industries, Inc. A single or a dual targetconfiguration can be employed to deposit a conductive layer of non-noblemetal alloys, such as certain nickel and chromium alloys. A targetcomprised of a non-noble metal alloy plate (such as is available fromTricor Industries Inc.) can be used. A vacuum chamber of the sputtercoater can be pumped down to base pressure of at least 10⁻⁵ Torr using adiffusion and mechanical pump combination. In other embodiments acombination of a mechanical pump, a turbo pump, a cryo pump, and/or anoil diffusion pump may be used. Magnetron sputtering cathodes housingthe non-noble metal alloy targets having a generally rectangular shapecan be energized using 2 KW power supplies (such as offered fromAdvanced Energy Inc.). An argon gas flow into the vacuum chamber can becontrolled (such as via a MKS model 1179A flow controller) to set asputtering pressure between 3 to 10 mTorr for use during the sputteringprocess.

Thickness and sheet resistance of the sputtered conductive layer can beefficiently controlled in-situ by controlling specific processparameters. Examples of process parameters include roll-to-roll webspeeds (i.e., controlling the speed of the substrate sheet as it travelsthrough the vacuum chamber during sputtering), power supplied to thesputtering targets (i.e. a product of the applied voltage and current tothe plasma formed near the target surface), gas pressure in thesputtering chamber, and the number of targets present in the chamber.For example, for sputtering of a conductive layer of a given alloy, theweb speed can be set to between 0.1 to 3.5 meters per minute andsputtering power density of from 1 to 8 Watts per square cm. Inembodiments, sputtered conductive layer of the alloy may be formedhaving a measured thickness value of about 25 nm and a sheet resistanceof about 45 ohms per square.

The resistive material layer can be deposited on top of the conductivelayer via one of the deposition techniques described above. For example,in one embodiment the resistive layer can be deposited using DCmagnetron sputtering from a carbon target. The thickness of theresistive material layer can be controlled by controlling specificprocess parameters. Examples of process parameters include roll-to-rollweb speeds (i.e., controlling the speed of the substrate sheet as ittravels through the vacuum chamber during sputtering), power supplied tothe sputtering targets (i.e., a function of the applied voltage andcurrent to the plasma formed near the target surface), gas pressure inthe sputtering chamber, and the number of targets present in thechamber. For example, in certain embodiments, for sputtering of aresistive layer on a given alloy, the web speed can be set to from 0.1to 3.5 meters per minute and sputtering power density of from 1 to 8Watts per square cm. In embodiments, the sputtered resistive layer maybe formed having a measured thickness value of about 1-200 nm.

In addition to the roll-to-roll process described above, biosensorcomponents can be manufacture using a scaled-up version of the samegeometry, using a large-scale roll-to-roll process. In such alarge-scale roll-to-roll process, maximum web speeds can be 0.1 to 10meters per minute, between 3 to 7 meters per minute, or higher than 10meters per minute. The large-scale roll-to-roll process may provide asputtering power density between 0.1 to 13, 2 to 10, or 5 to 8 Watts persquare cm. Additionally, the number of targets can include between 2, 4,6 or more, and the web width of the substrate sheet can be from 75 cm orlarger.

Embodiments additionally contemplate that physical vapor depositionprocesses can be utilized in which substrate sheets are held stationarywithin the vacuum chamber. Certain of such embodiments, are described indetail below in the Examples section. In some embodiments in which thesubstrate sheets are held stationary, deposition times for depositingthe conductive layer on the substrate sheets may be 5, 10, 15, 30minutes or more.

As previously noted above, biosensor components that include aconductive layer formed from the non-noble metal alloys and a resistivematerial layer, as described herein, can exhibit desirableelectrochemical properties that make them particularly well suited asreplacements for biosensor components that incorporate noble metals,such as palladium and/or gold. For instance, the biosensor components ofembodiments of the present disclosure may comprise a thin-film electrodeformed with a non-noble metal alloy conductive layer and a resistivematerial layer that exhibits desirable dose-response characteristicswhen undergoing chronoamperometry tests.

In various embodiments, the conductive layer can comprise nickel,chromium, and iron (in amounts as discussed above) and the conductivelayer and resistive material layer combination can have an oxidationwave voltage for Fe(II)[CN]₆ mediator (identified below asE_(peak,anodic)) of less than 400, or less than 390, or less than 380,or less than 375, or less than 360, or less than 350, or less than 340,or less than 330, or less than 325, or less than 320, or less than 310,or less than 300, or less than 290, or less than 280, or less than 275,or less than 270, or less than 260 millivolts (mV), as determined in aType 1 Linear Sweep Voltammetry Test (as discussed in the Examplessection).

This invention can be further illustrated by the following examples ofembodiments thereof, although it will be understood that these examplesare included merely for the purposes of illustration and are notintended to limit the scope of the invention unless otherwisespecifically indicated.

Examples Preparation of Thin-Film Electrodes

For each of the below-described examples (and comparative examples),biosensor components in the form of thin-film electrodes were formed bythe following-described physical vapor deposition process. It isunderstood that thin-film electrodes can be formed, using the belowprocess, to include a conductive layer of a plurality of different typesof elements and element alloys, such as the non-noble compositionslisted in Table 1. In most examples, these thin film electrodes alsoincluded a carbon resistive material layer that was deposited on top ofthe conductive layer, except where indicated otherwise. The processincluded forming thin-film electrode films by:

-   -   (a) metal or metal alloys were deposited on 10.16 cm×10.16 cm        square PET substrate sheet using direct current (“DC”) magnetron        sputtering in a high vacuum chamber, with the sputtering having        been performed with a Denton Vacuum Desktop Pro sputtering        device;    -   (b) the vacuum chamber was evacuated to an initial base pressure        of ˜10⁻⁵ Torr;    -   (c) argon gas of 10 sccm was introduced into the high vacuum        chamber to create a deposition pressure of 4 mTorr;    -   (d) the substrate sheets were rotated at approximately two        revolutions per minute within the vacuum chamber;    -   (e) a 5.08 cm diameter target of the metal or metal alloys was        held at a constant power of 40 Watts under the DC magnetron        sputtering device for deposition time of 15 minutes to coat at        least a portion of the substrate sheet with the conductive layer        (to initialize the targets, the targets were held at a constant        power of 40 Watts under the DC magnetron sputtering device for a        5 minute pre-sputtering time prior to the substrates being        introduced into the vacuum chamber);    -   (f) following the deposition of the conductive layer, carbon        layer was then deposited. A 5.08 cm diameter target of graphite        material was held at a constant power of 40 Watts under the DC        magnetron sputtering device for deposition time of 15 minutes to        coat at least a portion of the conductive layer (deposited in        step e) with a carbon layer (to initialize the targets, the        targets were held at a constant power of 40 Watts under the DC        magnetron sputtering device for a 5 minute pre-sputtering time        prior to the conductive layer coated substrate being introduced        into the vacuum chamber); and    -   (g) all depositions were carried out at room temperature.

Individual thin-film electrodes, with a size of 5.08 cm×7.62 cm, werecut from the thin-film electrode films that were formed by physicalvapor deposition, as provided above. Electrochemical experiments wereconducted using a Gamry Instruments Reference 600 potentiostat in athree electrode configuration, with the electrochemical cell containingthe thin-film electrode film positioned inside of a Gamry InstrumentsVistaShield Faraday Cage. Each of the thin-film electrodes was formed asa working electrode by partially masking the thin-film electrode withelectroplating tape having a single 3 mm diameter aperture die-cut intoit. As such, an unmasked portion formed by the die-cut aperture of thethin-film electrode provided a geometric working electrode surface areaof 0.0707 square cm. Another different area of unmasked portion of thethin-film electrode served as an electrical connection point to aworking electrode lead of the potentiostat. The masked portion of thethin-film electrode was placed onto a flat supporting block ofnon-conductive material, such as plastic. The thin-film electrode wasthereafter placed into a working electrode port of a glasselectrochemical cell. The exposed 3 mm diameter portion of the thin-filmelectrode was positioned near a center of a bottom opening of workingelectrode port of the electrochemical cell. The working electrode portof the electrochemical cell was sealed with a clamp and an O-ring. Theelectrochemical cell also contained a reference electrode comprising asaturated calomel reference electrode and a carbon auxiliary electrode.The reference electrode and the auxiliary electrode were placed,respectively in a reference electrode port and an auxiliary electrodeport. Additionally, the reference electrode and the auxiliary electrodewere connected, respectively, to a reference lead and an auxiliary leadof the potentiostat. The electrochemical cell also included a gas flowport by which to deaerate and blanket test solutions with inert gas,such as nitrogen.

Thin film electrodes were prepared from nickel and chromium alloys,having Ni to Cr ratios (by weight) of 100:0, 90:10, 85:15, 80:20, 72:28,60:40, 50:50, 40:60 and 0:100 according to the procedures discussedabove. The thin film electrodes having these conductive layers alsoincluded a carbon resistive layer prepared according to the proceduresdiscussed above. Carbon resistive layer thickness was approximately 15nm as determined by TEM imaging of cross-sectioned electrodes.

Type 1 Linear Sweep Voltammetry Test Description

A Type 1 Linear Sweep Voltammetry Test can be used to test theelectrochemical response of the thin-film electrodes. The Type 1 LinearSweep Voltammetry Test comprises the following steps: 50 mL of 10 mMpotassium phosphate buffer containing 145 mM sodium chloride at pH 7.1was placed into the electrochemical cell and the electrochemical cellwas sealed with stoppers. Gas inlet and outlet fittings, which wereassociated with the gas flow port, allowed inert gas sparging (i.e.,de-aerating) of the buffer solution, via a gas flow of nitrogen, using amedium-porous filter stick. The gas flow port additionally allowed thegas flow to be switched from the filter stick to a headspace-blanketingarrangement. The gas outlet was connected to an oil bubbler to preventback-diffusion of external gas (e.g., air) into the electrochemicalcell. The buffer solution was stirred with a magnetic stirbar whilesimultaneously sparged with nitrogen for at least 5 minutes beforeswitching the gas flow to a blanketing configuration. No agitation ofthe buffer solution from sparging or otherwise was otherwise presentduring the electrochemical experiments conducted via the Type 1 LinearSweep Voltammetry Test (i.e., the solution was quiescent duringelectrochemical testing).

A linear sweep voltammetry test was performed on the thin-film electrodethat comprised the working electrode within the electrochemical cell.The initial voltage potential for linear sweep voltammetry was 0 Vversus the open circuit potential (also known as the rest potential), asmeasured between the working electrode and the reference electrode(i.e., the saturated calomel reference electrode), and after a restperiod of at least 10 seconds prior to the voltammetric experiment, thevoltage potential was swept anodically at 25 mV per second until acurrent of at least 50 μA was observed. For solutions that containedFe(II)[CN]₆ mediator, the mediator was present at 1 mM concentration andthe linear sweep voltammetry conditions were otherwise identical tomediator-free solutions.

An peak voltage (“E_(peak,anodic)”) of the oxidation wave is determined,with such E_(peak,anodic) being defined as the voltage at which a localmaximum of current is observed as a result of the oxidation of anelectroactive species in solution, as measured between the workingelectrode and the counter electrode versus the reference electrode. Anillustration of an oxidation wave and an associated E_(peak,anodic), asobtained from a thin-film electrode using the Type 1 Linear SweepVoltammetry Test, is illustrated in FIG. 3. As can be seen from FIG. 3,the measured E_(peak,anodic) (or E-peak) value was approximately −76 mV,as measured versus a reference electrode.

Application of Type 1 Linear Sweep Voltammetry Test to Thin-FilmElectrodes

A plurality of different thin-film electrodes were tested using the Type1 Linear Sweep Voltammetry Test. In more detail, thin-film electrodesformed with NiCr 100:0 (or pure Ni), NiCr 90:10, NiCr 85:15, NiCr 80:20,NiCr 72:28, NiCr 60:40, NiCr 50:50, NiCr 40:60, and NiCr 0:100 (or pureCr), and each (nickel/chromium alloy) capped with an amorphous carbonresistive material layer, were tested.

The results of such tests for the alloys ranging from 72 to 90 weightpercent Ni are illustrated graphically in FIG. 4. It can be generallydesirable for the thin-film electrodes used in biosensors to exhibit apeak anodic current for Fe(II)[CN]₆ that occurs at a voltage as low aspossible. It can also generally be desirable for the thin-filmelectrodes used in biosensors to exhibit minimized and/or reducedcurrents under the influence of certain electrode potentials. FIG. 4 isa plot of a Type 1 linear sweep voltammetry test conducted on thin-filmelectrode of the various C on nickel/chromium alloys using a phosphatebuffer solution and a Fe(II)[CN]₆ mediator, and illustrates theheterogeneous electron transfer kinetics with the Fe(II)[CN]₆ mediatorfor these alloys as indicated by the voltage at which oxidation ofFe(II)[CN]₆ occurs. Generally, it may be desirable for an electrodematerial in a sensor such as a blood glucose sensor to have as fast aspossible heterogenous electron transfer kinetics so that the appliedoxidizing voltage that is required to operate the sensor is as small aspossible. In some embodiments, a biosensor may be operated at a voltagesufficiently anodic to cause the working electrode current to becontrolled by the diffusion of electroactive species (e.g., mediator).If the applied voltage is too oxidizing, oxidation of interferentspecies that might be present in blood, such as uric acid,acetaminophen, and the like, might be oxidized. This could result inundesired positive bias in the determined glucose concentration and aless accurate sensor. A review of FIG. 4 reveals that heterogeneouselectron transfer kinetics with ferrocyanide was generally acceptablefor each of the electrodes shown, with the NiCr 90:10 and NiCr 72:28having faster heterogeneous electron transfer than NiCr 85:15 and NiCr80:20.

All thin-film electrodes that were prepared were tested using the Type 1Linear Sweep Voltammetry Test on 3 replicate films for each NiCr alloyand an average E_(peak,anodic) value was determined for each of thedifferent NiCr alloys. The results of such tests for the alloys rangingfrom 0 to 100 weight percent Ni are illustrated graphically in FIG. 5.FIG. 5 is a plot of average E_(peak,anodic) value as a function ofweight % nickel in the NiCr alloy conductive layer. It can be generallydesirable for the thin-film electrodes used in biosensors to exhibit anE_(peak,anodic) current for Fe(II)[CN]₆ that occurs at a voltage as lowas possible. A review of FIG. 5 reveals that heterogeneous electrontransfer kinetics with ferrocyanide generally improves as the amount ofChromium increases.

FIG. 6 is a plot of a Type 1 linear sweep voltammetry test comparingthin-film electrodes of the C on nickel/chromium alloys having 40 weight% nickel and 80 weight % nickel, respectively, using a phosphate buffersolution and a Fe(II)[CN]₆ mediator. A review of FIG. 6 reveals thatheterogeneous electron transfer kinetics with ferrocyanide was fasterfor the NiCr alloy containing 40 weight % nickel compared to 80 weight %nickel.

Mechanical Flexibility Analysis Using Mandrel Bend Testing of Thin-FilmElectrodes

Mechanical flexibility of different films were analyzed using mandrelbend testing. The films that were tested were made according to theabove procedures and include NiCr alloy conductive layers of rangingfrom 40 to 100 weight % nickel, and each having a carbon resistivelayer.

Mandrel bend testing was carried out using the following apparatus:

-   -   a. Multimeter—A multimeter/ohmmeter capable of measuring        resistance to an accuracy of 0.01 ohms.    -   b. Probe—A resistance probe for measuring thin films that makes        contact with the film orthogonal to the long dimension of the        film in two locations contacting the full width of the film with        the contacts spaced two inches apart along the long axis.    -   c. Mandrels—Mandrels with diameters of ⅛″, ¼″, ½″, ⅝″ and having        surfaces than are smooth and clean and that are mounted on ball        bearings at each end so that the mandrel can rotate smoothly and        easily.

Mandrel testing was carried out by first examining the coating by eyeand ensuring that the coating surface was free of scratches, creases,wrinkles, and torn edges. The thin film electrode to be tested was cutinto a 2 inch wide strip and a length of at least 9 inches. Care wastaken to avoid any cracks while cutting the film.

The cut film was then tested as follows:

-   -   a. The initial sheet resistance (Ro) in ohms/sq was measured and        recorded using a 2 inch resistance probe along the length of        test sample, with measurements taken at 3 inch intervals.    -   b. The film was then bent around the ⅝″ mandrel so that the        coated side was in contact with the mandrel.    -   c. The ends of the film were held simultaneously and enough        tension was applied to the film to ensure firm contact with the        mandrel.    -   d. The film was pulled back and forth while carefully applying        gentle pressure on the film against the mandrel to let the        mandrel roll against the coating. Care was taken to make sure        that the film was rolling against the mandrel, not sliding, to        avoid scratches. The area of coating that was tested was marked.    -   e. Step d. was performed for 3 cycles or 6 strokes.    -   f. Sheet resistance (R) in ohms/sq was measured and recorded        using the 2 inch resistance probe along the length of test        sample length were the mandrel was contacted during the test,        with measurements taken at 3 inch interval over the test area.

The results of the mandrel testing with a comparison of the final sheetresistance (R) to initial sheet resistance (R₀) are shown in FIG. 7. Areview of FIG. 7 reveals that the films having conductive layers of NiCralloys having 85 to 100 weight percent nickel had lower mechanicalstability than the films having conductive layers of NiCr alloys having40 to 80 weight percent nickel, especially with the smaller diametermandrels. Thin film electrodes that have better relative mechanicalintegrity as demonstrated by this test are believed to be more desirablefor improved manufacturing robustness of web and sheet-based processes.When comparing two films using the mandrel tests described above, it isbelieved that the better performing film is indicative of more robustmechanical performance and improved repeatability and consistency forprocessing and using the thin-film electrode film in biosensorapplications.

The above detailed description of embodiments of the disclosure isintended to describe various aspects of the invention in sufficientdetail to enable those skilled in the art to practice the invention.Other embodiments can be utilized and changes can be made withoutdeparting from the scope of the invention. The above detaileddescription is, therefore, not to be taken in a limiting sense. Thescope of the present invention is defined only by claims presented insubsequent regular utility applications, along with the full scope ofequivalents to which such claims are entitled.

In this description, references to “one embodiment,” “an embodiment,” or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment”, “an embodiment”, or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Forexample, a feature, step, etc. described in one embodiment may also beincluded in other embodiments, but is not necessarily included. Thus,the present technology can include a variety of combinations and/orintegrations of the embodiments described herein.

The inventors hereby state their intent to rely on the Doctrine ofEquivalents to determine and assess the reasonably fair scope of thepresent disclosure as it pertains to any apparatus not materiallydeparting from but outside the literal scope of the invention as setforth in the following claims.

Definitions

It should be understood that the following is not intended to be anexclusive list of defined terms. Other definitions may be provided inthe foregoing description, such as, for example, when accompanying theuse of a defined term in context.

As used herein, the terms “a,” “an,” and “the” mean one or more.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itselfor any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination, B and C in combination; orA, B, and C in combination.

As used herein, the terms “comprising,” “comprises,” and “comprise” areopen-ended transition terms used to transition from a subject recitedbefore the term to one or more elements recited after the term, wherethe element or elements listed after the transition term are notnecessarily the only elements that make up the subject.

As used herein, the terms “having,” “has,” and “have” have the sameopen-ended meaning as “comprising,” “comprises,” and “comprise” providedabove.

As used herein, the terms “including,” “include,” and “included” havethe same open-ended meaning as “comprising,” “comprises,” and “comprise”provided above.’

Numerical Ranges

The present description uses numerical ranges to quantify certainparameters relating to the invention. It should be understood that whennumerical ranges are provided, such ranges are to be construed asproviding literal support for claim limitations that only recite thelower value of the range as well as claim limitations that only recitethe upper value of the range. For example, a disclosed numerical rangeof 10 to 100 provides literal support for a claim reciting “greater than10” (with no upper bounds) and a claim reciting “less than 100” (with nolower bounds).

1. A biosensor component for use in analyzing a biological sample, saidbiosensor component comprising: a substrate; a conductive layerdeposited on said substrate; a resistive material layer deposited onsaid conductive layer; and a biological reactant for electrochemicallyreacting with said biological sample, wherein said conductive layercomprises nickel and chromium, wherein a combined weight percent of thenickel and chromium in the conductive layer is in the range of 50 to 100weight percent, and wherein the weight percent of chromium in theconductive layer is greater than 20 weight percent or wherein thethickness of the resistive layer is less than 20 nm.
 2. The biosensorcomponent according to claim 1, wherein said biosensor componentcomprises an electrode, wherein said electrode is a working electrode ora reference electrode or a counter electrode.
 3. The biosensor componentaccording to claim 1, wherein the biosensor is a blood glucose sensor.4. The biosensor component according to claim 1, wherein said biosensorcomponent comprises a test-strip.
 5. The biosensor component accordingto claim 1, wherein said substrate has a thickness between 25 and 500μm, and said conductive layer has a thickness between 15 and 200 nm. 6.The biosensor component according to claim 1, wherein said conductivelayer is sputtered on said substrate and said resistive material layeris sputtered on said conductive layer.
 7. The biosensor componentaccording to claim 1, wherein the weight percent of chromium in theconductive layer is in the range from about 25 to about 95 weightpercent; and wherein the balance of the conductive layer is essentiallynickel; and wherein the resistive material layer has a thickness between5 and 200 nm.
 8. The biosensor component according to claim 7, whereinthe weight percent of chromium in the conductive layer is in the rangefrom about 40 to about 95 weight percent; and wherein the balance of theconductive layer is essentially nickel; and wherein the resistivematerial layer has a thickness between 5 and 200 nm.
 9. The biosensorcomponent according to claim 8, wherein the weight percent of chromiumin the conductive layer is in the range from greater than 50 to about 95weight percent; and wherein the balance of the conductive layer isessentially nickel; and wherein the resistive material layer has athickness between 5 and 200 nm.
 10. The biosensor component according toclaim 1, wherein the resistive layer is amorphous carbon.
 11. Thebiosensor component according to claim 1, wherein the resistive materiallayer has a thickness between 5 and 30 nm.
 12. The biosensor componentaccording to claim 1, wherein the combined weight percent of the nickeland chromium in the conductive layer is in the range of 90 to 100 weightpercent, and wherein the thickness of the resistive layer is between 5and less than 20 nm.
 13. (canceled)
 14. The biosensor componentaccording to claim 12, wherein the resistive material layer has athickness between 5 and 15 nm.
 15. The biosensor component according toclaim 1, wherein said substrate comprises a flexible, non-conductivefilm.
 16. The biosensor component according to claim 1, wherein saidbiosensor component has a visible light transmission of no more than20%.
 17. A method for forming an electrode for a biosensor comprising:(a) providing a substrate; (b) providing a conductive material target;(c) physical vapor depositing at least a portion of said substrate withmaterial from said conductive material target to thereby form aconductive layer on said substrate; (d) providing a resistive materialtarget; and (e) physical vapor depositing at least a portion of saidconductive layer with material from said resistive material target tothereby form a resistive material layer on said conductive layer;wherein said conductive layer comprises nickel and chromium, wherein acombined weight percent of the nickel and chromium in the conductivelayer is in the range of 50 to 100 weight percent, and wherein theweight percent of chromium in the conductive layer is greater than 20weight percent or wherein the thickness of the resistive layer is lessthan 20 nm.
 18. The method of claim 17, wherein said substrate comprisepolyethylene terephthalate (PET), wherein said substrate has a thicknessin the range from 25 and 500 μm, said conductive layer has a thicknessof in the range from 15 and 200 nm, and said resistive material layerhas a thickness in the range from 5 to 100 nm, wherein said electrodehas a visible light transmission of no more than 20%, wherein thebiosensor comprises a blood glucose sensor.
 19. The method of claim 18,wherein the weight percent of chromium in the conductive layer is in therange from about 25 to about 95 weight percent; and wherein the balanceof the conductive layer is essentially nickel.
 20. The method of claim19, wherein the resistive layer is amorphous carbon.
 21. The method ofclaim 19, wherein said substrate comprise polyethylene terephthalate(PET), wherein said resistive material layer comprises amorphous carbonand has a thickness in the range from 5 to 20 nm.